Field of the Invention
The present invention relates to an image processing method of estimating a blur as a deterioration component acting on a blurred image based on a single blurred image.
Description of the Related Art
Recently, according to the enhancement of high definition of a display apparatus, the improvement of the image quality of a captured image is required. Due to a deterioration factor such as an aberration or a diffraction of an optical system used for photography or a hand shake during the photography, the captured image loses information of an object space. Accordingly, a method of correcting the deterioration of the captured image based on these factors to obtain a high-quality image is previously proposed. As such a method, for example, there is a method of using Wiener filter or Richardson-Lucy method. However, in each of these method, a high correction effect cannot be obtained if a deterioration component (blur) acting on an image is not known.
On the other hand, previously, a method of estimating a hand shake component based on a single image deteriorated by the hand shake is proposed. U.S. Pat. No. 7,616,826 discloses a method of estimating the hand shake component in the image deteriorated by the hand shake by using statistical information relating to a strength gradient distribution of a known natural image. The natural image means an image where modern people naturally see for living. Accordingly, the natural image includes not only an image of trees or animals, but also an image of humans, architectures, electronic devices, or the like. As a characteristic of the natural image, it is known that a histogram (strength gradient histogram) relating to a strength gradient of a signal follows a heavy tailed distribution depending on the strength of the gradient. U.S. Pat. No. 7,616,826 discloses a method of applying a restriction where the strength gradient histogram of the hand-shake-corrected image follows the heavy tailed distribution to estimate a hand-shake-corrected image based only on the hand shake image. A blur component is estimated based on a comparison result between the hand-shake-corrected image and the hand shake image. In this case, the estimation accuracy of the blur component improves with increasing the number of edges included in the hand shake image.
However, the edge amount in the blurred image depends on a structure of a photographed object. Accordingly, the edge amount which is sufficient for the estimation does not always exist in the image. In particular, when a shape of the blur varies depending on an area in the image (called Shift-variant), it is necessary to estimate the blur only by using a specific partial area in the blurred image, and accordingly the edge amount tends to be insufficient. In an area where signal changes such as edges and textures are small, the estimation accuracy of the blur is extremely deteriorated. When the estimation method disclosed in U.S. Pat. No. 7,616,826 is used for the area, a large amount of error occurs in the estimated hand shake component. The same is true on a diffraction, an aberration, a defocus, and a disturbance, other than the hand shake (these deterioration factors are collectively called a “blur”).